Different conditions for the cultivation of Pinus strobus root-hypocotyl explants were studied for the production of ectomycorrhizae in vitro. Moisture content of the culture medium used for growing seedlings before excision was critical and a low level of moisture during this period led to a slow and erratic growth of the explants. During short-term experiments (6 weeks) no vitamins or inositol requirements could be detected but under the same conditions auxins improved growth significantly whereas kinetin did not. The optimum NAA concentration was about 2 × 10−7 M in the absence of exogenous kinetin. The requirement for a piece of hypocotyl might not be absolute because some evidence was obtained that auxin in the organic medium might, partially, replace it. Whereas virtually no growth took place with 5% sucrose in the organic medium, optimum concentration for root elongation was found to be between 11 and 15%. During the 2 first weeks following excision the rate of growth remained low (1.2 mm week−1) but between the 2nd and the 6th weeks it reached 6.3 mm week−1 before dropping back to 2.3 mm week1 between the 6th and the 10th weeks. Some typical ectomycorrhizae showing mantle and Hartig's net were obtained upon inoculation with ectomycorrhizal fungi, but more research is needed before the method can be recommended for general use in studies on the physiology of ectomycorrhizae.